Medical monitoring systems have greatly improved over the past thirty years. There is, however, much room for improvement, particularly in the manner in which the medical data is presented to the physician. For example, it has been estimated that in the United States between 2,000 and 10,000 patients die every year from causes related to anesthesia, a field in which the present invention is especially useful. Anesthesia-related accidents are typically caused by human error, equipment failure, surgical events, or unexpected alterations in the patient's homeostasis. It is believed that many accidents could be avoided by transforming, in real time, the plethora of information provided to the physician into a more manageable tool for assisting the physician in making a diagnosis of the patient's current condition.
Although equipment failure still causes some accidents, the greatest number of anesthesia-related accidents can be attributed to human error. The process of selecting the correct treatment is performed by the physician under stress, under high mental load and in conditions of uncertainty. Inexperience and fatigue can further undermine the physician's performance. Moreover, the variable and idiosyncratic nature of the patient's physiology contributes substantially to the complexity of the environment. It has been concluded that monitors need to be observed at least every thirty seconds in order for critical events to be detected at an early stage. The physician must divide his or her attention among treating the patient, observing the scattered and intermittent data and monitoring the surgical field. This can cause a delay in the detection and treatment of dangerous conditions.
More than thirty different physiological parameters (e.g., heart rate, blood pressure, cardiac output) are typically measured in the operating room or intensive care unit (ICU) by a number of medical monitors. The medical monitors currently in use are prone to generate false alarms, reducing the physician's responsiveness. A further problem with such monitors is that the data is presented in a confusing manner, i.e., many disparate parameters are displayed in various locations around the physician. Newer monitoring systems integrate the functions of several monitors in one unit, however these provide a congested, confused display. In addition, these monitors have a limited signal processing capability, so their display, which is of short duration, is presented after a time delay.
The dynamic nature of the operating room or ICU environment underscores the need for a system for rapidly presenting useful and comprehensible information to the physician, and quick reaction by the physician, to prevent undesired consequences to the patient. In addition, the physician should be able to identify the primary effector whenever there is a change in the patient's status. This is because knowledge of the primary effector, or the first physiological parameter that varies from its baseline (homeostatic) state, may reveal the patient's true problem. An inability to rapidly detect which physiological parameter first varies from its baseline state may prevent the optimal, causal directed, treatment from being provided.
The aforementioned paper outlines a system that overcomes some of the above-described shortcomings of known medical monitoring systems. Referring to FIG. 1, this system comprises a variety of sensors 10 adapted to be attached to a patient being monitored, a plurality of medical monitors 12 for measuring a plurality of medical parameters indicative of the condition of the patient, a data acquisition module 14, a feature extracting module 16, a vital function unit (VFU) 18, a reference value unit 20, an adaptive inference unit (AIU) 22, and a display 24. The medical monitors 12 are interfaced with the vital function unit 18 by the data acquisition module 14 and feature extraction module 16. The data acquisition module 14 runs as a separate background module that collects and transfers the data to the feature extraction module 16. The feature extraction module 16 extracts relevant features (maximum value, minimum value, etc.) from all input values (heart rate, blood pressure, etc.). All of the collected data is transferred to the AIU 22 and VFU 18. One embodiment of this system has been developed on a 386/33 Mhz platform equipped with an 80387 mathematical co-processor.
The vital function unit 18 is the subsystem that has been developed to facilitate the early identification of the patient's physiological changes. The operation of the VFU 18 is based on the fundamental concept of homeostasis. Under this concept, the patient is regarded as an aggregate of interdependent subsystems (cardiovascular, respiratory, etc.) that interact with each other. It is recognized that a malfunction of one subsystem may cause another subsystem to malfunction as well, and that yet another subsystem may react so as to complicate or mask these malfunctions. The physician is presented a set of physiological parameters (data) that have departed from their baseline values.
The physician usually first attempts to evaluate the severity of the patient's status and to determine whether the patient's condition has improved or deteriorated and to what extent and at what speed any changes have occurred. The assessment of severity should not be confused with the diagnosis, which is the next step and requires more time. All of the parameters are equally important in detecting changes in the patient's condition. In assessing the severity of the patient's status, the direction of deviation of a specific parameter is relatively unimportant; however, the extent and rate of change are important. The direction of deviation is more meaningful in making the correct diagnosis, while the extent and rate of, change are less important.
The primary task of the VFU 18 is to produce a new indicator, the vital function status (VFS) indicator. Another task of the VFU is to identify the first parameter that deviated from its baseline state. The measured and the calculated values of all the physiological parameters are compared to reference values stored in the reference value unit 20. The values in the reference value unit 20 may be pre-implemented in the system, with different values being assigned in accordance with the patient's age and/or specific problems (for example, hypertension). The physician is able to select specific reference values for each parameter. In other words, the system will utilize for blood pressure the appropriate reference values for hypertension if the patient is a young hypertensive adult, yet reference values for other parameters will be based upon the patient's age group, without consideration of the hypertension.
Each parameter is assigned one of six levels of danger, ranging from zero to 5 according to the following scale:
0=no danger PA1 1=caution PA1 2=alert PA1 3=serious PA1 4=severe PA1 5=critical danger.
FIG. 2 is an example of a display provided by the system. All of the calculated functions are merged to produce the VFS, a numeric indicator whose value similarly ranges from zero to 5, using the scale described above. The graphically displayed VFS indicator provides a semi-quantitative overall assessment of the patient's status. The display comprises a first graph 30 that depicts the history of the VFS over a two minute time span and is periodically updated, for example every second. A second graph 32 depicts the history of the VFS over the last thirty minutes and is also updated every second. Each plot is divided into six equal horizontal arrays, each array having a different color. A text message 34 appears in a third window; this message identifies the first parameter that deviated from its baseline.
The above-described system and its associated display provide a framework for a system with which the physician could detect the nature of a problem in evolution. Moreover, undesired conditions could be anticipated and quickly treated. However, one shortcoming of the system is that it lacks an efficient and effective method for transforming the measured data into the single VFS indicator. The present invention provides this missing element.